Machine operators often apply retarding devices and select gearing to control speed during downhill conditions. US Patent Application Publication 2008/0207398 (the '398 publn) discloses the use of an orientation sensor to control the retarding of an engine through operation of a hydraulic driven fan. The '398 publn, however, fails to disclose a system to determine a target speed. The '398 publn also fails to disclose a system to control a downhill speed through powertrain retarding and transmission gear control.